Neutering/spaying litter mates

Hi. I am collecting two dwarf lion lops in 4 weeks time, girl and boy litter mates. They will be 8 weeks old. I am trying to figure out if they need separating. We will get the boy neutered ASAP, hopefully at 10 weeks, and have been told that he will still be able to reproduce for 4 weeks. Firstly, is this still the case if he is neutered at 10/12 weeks and secondly, would the female be able to get pregnant during those 4 weeks seeing that she will only be 14/16 weeks old? I will separate them if necessary but don’t want to if it’s not needed.
Thanks for reading.